Field of the Invention
The present invention relates to a hydrostatic continuously variable transmission including a neutral biasing mechanism that can change an angle of a swash plate by performing an operation of pivoting a trunnion shaft, and that biases the swash plate to a neutral position.
Description of the Related Art
For example, JP 2011-152823A describes a conventional hydrostatic continuously variable transmission. The hydrostatic continuously variable transmission described in this publication includes a cam member (in this publication, a “cam plate”) in a neutral biasing mechanism, the cam member being integrally attached to a trunnion shaft and has a cam portion (in this publication, a “cam recess portion”) formed so as to recede toward the trunnion shaft side. Furthermore, this neutral biasing mechanism includes a pivot arm (in this publication, an “L-shaped arm) that pivots around a rocking shaft parallel with the trunnion shaft, and a roller that is rotatably supported by the pivot arm and pivots the cam member to a neutral posture corresponding to the neutral position by being fitted into the cam portion.
Furthermore, the neutral biasing mechanism includes a single spring that is attached so as to be spanned from the pivot arm to a base and biases the pivot arm such that the roller is fitted into the cam portion.
Incidentally, in the hydrostatic continuously variable transmission, there are cases where biasing force of the neutral biasing mechanism decreases as a result of the spring undergoing plastic deformation after being used for years, for example.
In such cases, the biasing force of the neutral biasing mechanism becomes smaller than the force necessary for restoring the swash plate to the neutral position, and the swash plate is then difficult to be restored to the neutral position, resulting in inconvenience.
In the conventional neutral biasing mechanism, the swash plate is biased to the neutral position by only the biasing force of a single spring that is attached to a fixed position. Accordingly, in order to change the biasing force of the neutral biasing mechanism, the single spring needs to be replaced, which requires time and effort. Moreover, since the spring is replaced, the biasing force cannot be finely adjusted, and therefore many kinds of springs need to be prepared.
In view of the foregoing situation, provision of a hydrostatic continuously variable transmission has been desired that can easily change the biasing force of the neutral biasing mechanism for restoring the swash plate to the neutral position, with a simple structure.